1. Field of the Invention
The invention relates to the control of fluid flow into a wellbore. More particularly, the invention relates to a flow control apparatus that compensates for pressure differentials along a wellbore.
2. Background of the Related Art
In hydrocarbon wells, horizontal wellbores are formed at a predetermined depth to more completely and effectively reach formations bearing oil or other hydrocarbons in the earth. Typically and as shown in FIG. 1, a vertical wellbore 102 is formed from the surface of a well 100 and thereafter, using some means of directional drilling like a diverter, the wellbore is extended along a horizontal path. Because the hydrocarbon bearing formations can be hundreds of feet across, these horizontal wellbores 104 are sometimes equipped with long sections of screened tubing 106 which consists of tubing having apertures therethough and covered with screened walls, leaving the interior of the tubing open to the inflow of filtered oil.
Along the length of a horizontal wellbore 104, a pressure drop occurs between the toe 108, or end of the wellbore and the heel portion 110 thereof due primarily to friction looses in fluid traveling through the wellbore. Over time, the lower pressure of the fluid at the heel of the wellbore 104 causes a correspondingly lower fluid pressure in the formation adjacent the heel. The result is a xe2x80x9cconingxe2x80x9d effect whereby fluid in the formation tends to migrate toward the heel 110 of the wellbore, decreasing the efficiency of production over the length of the horizontal wellbore. The path of fluid in such a condition is illustrated by arrows 101 in FIG. 1.
In an attempt to equalize the fluid pressure across a horizontal wellbore, various potential solutions have been developed. One example is the EQUALIZER(trademark) production management system manufactured and sold by Baker Oil Tools of Houston, Tex. The EQUALIZER(trademark) device incorporates a helical channel as a restrictor element in the inflow control mechanism of the device. The helical channel surrounds the inner bore of the device and restricts oil to impose a more equal distribution of fluid along the entire horizontal wellbore. However, such an apparatus can only be adjusted at the well surface and thereafter, cannot be re-adjusted to account for dynamic changes in fluid pressure once the device is inserted into a wellbore. Therefore, an operator must make assumptions as to the well conditions and pressure differentials that will be encountered in the reservoir and preset the helical channel tolerances according to the assumptions. Erroneous data used to predict conditions and changes in the fluid dynamics during downhole use can render the device ineffective.
A variation of the same problem arises in the operation of gas injection wells. Under certain conditions, it is necessary to provide artificial forces to encourage oil or other hydrocarbons into a wellbore. One such method includes the injection of gas from a separate wellbore to urge the oil in the formation in the direction of the production wellbore. While the method is effective in directing oil, the injection gas itself tends to enter parts of the production wellbore as the oil from the formation is depleted. In these instances, the gas is drawn to the heel of the horizontal wellbore by the same pressure differential acting upon the oil. Producing injection gas in a hydrocarbon well is undesirable and it would be advantageous to prevent the migration of injection gas into the wellbore.
There is a need therefore, for a flow control apparatus for downhole use in a wellbore that compensates for the dynamic changes and differences in fluid pressure along the length of the wellbore. There is a further need, for a flow control apparatus for use in a wellbore that is self-regulating and self-adjusts for changes in pressure differentials between an oil bearing formation and the interior of the apparatus. There is yet a further need for a flow control apparatus that prevents the introduction of unwanted gasses and fluids into a wellbore but allows the passage of oil therethrough. There is yet a further need for a flow control apparatus that will prevent the migration of unwanted fluids into a wellbore after the oil in a formation therearound is depleted. There is still a further need for a flow control apparatus that can be controlled remotely based upon well conditions in a wellbore or in the formation therearound.
The present invention provides an apparatus for use in a hydrocarbon producing wellbore to compensate for pressure differentials between fluid in the wellbore and fluid in an oil bearing formation therearound. In one aspect of the invention, a perforated inner tube is surrounded by at least one axially movable member that moves in relation to pressure differentials between fluid inside and outside of the apparatus. The movable member selectively exposes and covers the perforations of the inner tube to pass or choke fluid moving into the apparatus from the wellbore. In another aspect of the invention, an apparatus is provided for insertion in a string of screened tubing in a horizontal wellbore. The apparatus includes an inner tubular body portion having apertures in the wall thereof for passing oil, an outer tubular body and a pathway therebetween permitting oil from a formation to migrate into the inner body. Disposed around the inner body is an annular sleeve having apertures formed therethrough, the apertures constructed and arranged to align with the apertures of the inner body, thereby permitting fluid to flow therethough. In one embodiment, the sleeve member is spring biased on the inner body, and includes a piston surface acted upon by fluid entering an annular area between the annular sleeve and the outer body. In the presence of a pressure differential between the fluid in the formation and the fluid inside the apparatus, the apparatus is designed to restrict the flow of oil into the wellbore. Specifically, the piston surface is deflected by a mass flow rate brought about by a pressure differential. As the piston is deflected, the apertures of the body and the sleeve become increasingly misaligned, preventing most inflow of fluid into the body when the piston is completely actuated. The flow of fluid into the apparatus therefore, is inversely related to the pressure differential between the inside and outside of the apparatus. In another aspect of the invention, more than one apparatus is placed in series in a wellbore to compensate for pressure differential over a predetermined length of the wellbore. In another aspect of the invention, the apparatus is at least partially controlled by regulating and manipulating the pressure in a formation that is acted upon by an injection gas.
So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.